Three-Dimensional Distribution of Limonin, Limonoate A-Ring Monolactone, and Naringin in the Fruit Tissues of Three Varieties of Citrus paradisi

Limonin and naringin are the two major bitter compounds in Citrus paradisi (grapefruit), and tissue-specific patterns of their distribution are well-established. This study was undertaken to determine the distribution of these compounds within Duncan, Marsh, and Thompson Pink tissues using three-dimensional fruit dissection (600−900 samples per fruit) and highly specific radioimmunoassays for limonin and naringin quantification. Results from a GLM ANOVA showed that there was no radial distribution pattern of limonin or naringin accumulation in these fruit. There were statistically significant differences in the axial distribution of these compounds within the fruit tissues. The limonin concentration in flavedo, albedo, outer segment membrane, and juice vesicles increased toward the distal end of the fruit. Naringin concentrations in flavedo, albedo, and outer segment membranes tended to be higher in the center portion of the fruit. Limonoate A-ring monolactone levels are also reported. Keywords: Grapefruit; limonin; limonoate A-ring monolactone; naringin; axial distribution